Determination Of Selenium Research Articles

Extractive separation of selenium for atomic-absorption determination in purified sulfur

The expanding use of sulfur in medicine, science and technology has tightened the requirements for the impurity composition, including the content of selenium in sulfur. Combined extraction-atomic absorption methods have been developed to determine selenium in purified sulfur. The possibility of using thiourea derivatives such as sodium diethyldithiocarbamate and diphenylthiocarbazone for the extraction of microgram amounts of selenium from sulfuric acid solutions was studied. Optimal conditions for the extraction of selenium from sulfate solutions are determined. Two procedures for selenium separation are proposed: extraction of selenium diethyldithiocarbamate with ethyl acetate from a solution of sulfuric acid with pH 3 or extraction of selenium dithizonate with chloroform from a 5.25 – 6.0 M sulfuric acid solution. The results of the extraction-atomic absorption determination of selenium in sulfur are compared for both procedures of selenium separation. The accuracy of the selenium determination in purified sulfur is confirmed by the method of varying sample weight. The optimal temperature-time parameters for the electrothermal atomic absorption determination of selenium are determined. The limit of selenium determination is 1 × 10–5 % wt. The values of sr in the range of selenium content 2 × 10–5 — 1 × 10–4 % wt. change from 0.10 to 0.12.

Ultrasensitive determination of selenium in foodstuffs and beverages using an electroanalytical approach

This work describes the development of an electroanalytical methodology to the determination of nanomolar levels of selenium, which is sensitivity, selectivity, simple, low cost, quickness, and robustness. Therefore, it was employed a silver solid amalgam electrode modified by a thin and stable mercury film (f-AgSAE) allied to square-wave cathodic adsorptive stripping voltammetry (SWCASV). Besides this, the adsorptive and square-wave voltammetry parameters were previously optimized following the built of analytical curves in the linear range from 1.00 × 10−7 to 8.00 × 10−6 mol L−1, that resulted in a correlation coefficient of 0.9989, repeatability of 1.64%, reproducibility of 4.90%, detection limit of 1.01 × 10−9 mol L−1 and quantification of 3.36 × 10−9 mol L−1. This methodology proposed can be compared with similar data obtained by sophisticated spectroscopic techniques and other electroanalytical techniques. The procedure proposed was applied to selenium determination in in natura food (apple, orange, potato, spinach and tomato) and beverage (coconut water, soy juice and soy milk) samples. These samples were digested using a simple procedure that resulted in very satisfactory recovery percentages, confirming suitable robustness of the proposed methodology.

Determination of selenium and copper in water and food by hierarchical dendritic nano-gold modified glassy carbon electrodes.

The sensitive determination of selenium and copper is of importance for environmental monitoring and food safety. A stripping voltammetric determination of selenium and copper in water and selenium-rich foods was developed using hierarchical dendritic gold nanostructure (AuHD) modified glassy carbon electrodes (GCE). The AuHD thin films were electrodeposited potentiostatically onto the GCE from a solution containing 25 mM HAuCl4 and 0.1 M Na2SO4 at -0.6 V for 20 min. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) studies showed that the electrodeposited gold thin film shows a nanoforest-like morphology with a thickness of about 30-40 μm and a hierarchical dendritic structure with primary-, secondary-, and higher-order branches. Se(iv) and Cu(ii) in a 0.1 M H2SO4 solution were determined by square-wave anodic stripping voltammetry using the AuHDs/GCE as the working electrode. Prior to anodic stripping, Se(iv) and Cu(ii) were accumulated onto the working electrode surface at -0.2 V for 300 s. The stripping peak currents of Se(iv) at 0.81 V and Cu(ii) at 0.31 V were positively correlated with the concentrations of Se(iv) and Cu(ii) in a range of 50-700 nM. The limits of detection (3σ) for Se(iv) and Cu(ii) were 1.4 nM and 3.7 nM, respectively. The accuracy of the method was verified by analysing certified water standard reference materials, and the results showed that the method has good accuracy and high precision. The method was used to determine selenium and copper in tap water, selenium-rich rice and selenium-rich eggs. The results were compared with those obtained by using inductively coupled plasma-mass spectrometry (ICP-MS) and found to be consistent with those of ICP-MS. The proposed method had the advantages of simplicity, rapidity, good reproducibility, and high sensitivity and it can be used for the analysis of real samples.

Determination of selenium in food and environmental samples by hydride generation high-resolution continuum source quartz furnace atomic absorption spectrometry

The paper presents a method for Se determination in a wide variety of food and environmental samples by hydride generation high-resolution continuum source quartz furnace atomic absorption spectrometry.

Erratum to: Determination of Selenium in Drinking Water by Electrothermal Atomic Absorption Spectrometry after Photochemical Generation, Distillation, and Preconcentration of Its Gaseous Compounds in a Graphite Furnace

An Erratum to this paper has been published: https://doi.org/10.1134/S1061934821330017

Determination of Total and Inorganic Selenium in Selenium-Enriched Rice, Tea, and Garlic by High-Performance Liquid Chromatography–Inductively Coupled Plasma Mass Spectrometry (HPLC-ICP-MS)

The total selenium content of selenium-enriched agricultural products was determined by inductively coupled plasma mass spectrometry after microwave digestion. The total selenium content in the tested samples ranged from 27.9 μg/kg to 13.6 mg/kg. High performance liquid chromatography–inductively coupled plasma mass spectrometry was employed to determine selenite and selenate in selenium-enriched rice, tea, and garlic. The separation of inorganic and organic selenium was realized within 15 min by using 40 mmol/L diammonium phosphate (pH 5.0) and 60 mmol/L diammonium phosphate (pH 6.0) as the mobile phase with gradient elution. Selenite and selenate were isolated by ultrasonic assisted extraction at 78 °C for 30 min with 0.1 mol/L potassium hydroxide as the extraction solution. The detection limits were 2.5 and 5 μg/kg for selenite and selenate, respectively. The relative standard deviation was less than 5.5%. Recoveries of inorganic selenium were between 88.2% and 113.0%. The proposed method was successfully applied for the determination of inorganic selenium as well as total selenium in selenium-enriched rice, tea, and garlic. The results showed that inorganic selenium in natural selenium-enriched agricultural products is primarily present in selenite composing no more than 20% of total selenium.

Determination of Selenium in Drinking Water by Electrothermal Atomic Absorption Spectrometry after Photochemical Generation, Distillation, and Preconcentration of Its Gaseous Compounds in a Graphite Furnace

A highly sensitive scheme of the determination of selenium in drinking water by electrothermal atomic absorption spectrometry with the on-line preconcentration of gaseous analyte compounds obtained by the UV treatment of an analyzed solution in a graphite furnace (GF) is implemented. A photochemical generator of original design of the type “UV lamp in a hollow cylindrical reactor” is used. The conditions of the photochemical generation and sorption of gaseous selenium compounds are optimized. The efficiency of a number of permanent sorbent modifiers, such as, metallic iridium, tungsten and zirconium carbides, and mixtures of tungsten and zirconium carbides with activated carbon, at the sorption stage in the GF is estimated. The maximum analytical signals of selenium are recorded using graphite tubes modified by iridium. The analytical scheme is verified by a spike recovery test, the recovery of element additives was 90%. The attained limit of detection for Se(IV) is 4.1 ng/L; the relative standard deviation of the results of replicate determinations is no more than 4.0% at the concentration of Se(IV) in water samples 0.1 µg/L.

Preconcentration of hydrogen selenide using hydride generation and purge-and-trap collection for the determination of selenium in water samples by atomic absorption spectrometry

ABSTRACT Gaseous hydrogen selenide (H2Se) generated by the addition of sodium tetrahydroborate (NaBH4) into an acidic aqueous sample was collected using an aqueous ammonia solution. The selenium (Se) concentration was determined using graphite furnace atomic absorption spectrometry (AAS). Several experimental conditions, such as the type of the collection solution, volume of NaBH4 and hydrochloric acid, and collection time, were optimized. In addition, the effect of coexisting ions was quantitatively evaluated and eliminated. The limit of detection for Se in a standard water sample was 1.3 ng/mL. The additional recovery of spiked Se in tap water and river water samples ranged from 98 ± 2.4 to 100 ± 2.2%. The proposed method facilitates simple and sensitive analysis for Se in water samples without H2Se gas generator for AAS.

Sorption of Se (IV) from aqueous solutions with subsequent determination by X-ray fluorescence analysis

An approach to sorptive separation of Se (IV) from solutions on a novel S,N-containing sorbent with subsequent determination of the analyte in the sorbent phase by micro-x-ray fluorescence method is presented. The sorbent copolymethylenesulfide-N-alkyl-methylenamine (CMA) was synthesized using «snake in the cage» procedure and proven to be stable in acid solutions. Conditions for quantitative extraction of Se (IV) were determined: sorption in 5 M HCl or 0.05 M HNO3 solutions when heated to 60°C, phase contact time being 1 h. The residual selenium content in the solution was determined by inductively coupled plasma mass spectrometry (ICP-MS) using 82Se isotope. The absence of selenium losses is proved and the mechanism of sorption interaction under specified conditions is proposed. The method of micro-x-ray fluorescence analysis (micro-RFA) with mapping revealed a uniform distribution of selenium on the sorbent surface. The possibility of determining selenium in the sorbent phase by micro-RFA is shown. When comparing the obtained results with the results of calculations by the method of fundamental parameters, it is shown the necessity of using standard samples of sorbates to obtain correct results of RFA determination of selenium in the sorbent phase.

Determination of selenium in food and environmental samples using a gold nanocages/fluorinated graphene nanocomposite modified electrode

Selenium is one of the most attractive nutrient elements for antioxidant, anticancer and immunomodulatory effects, which is obtained from the agricultural food and environment. Herein, a gold nanocages/fluorinated graphene (AuNCs/FG) nanocomposite modified glassy carbon electrode (GCE) was fabricated for the electrochemical determination of selenium by square wave anodic stripping voltammetry. Under the optimal parameters, a wide linear relationship between peak current of selenium on AuNCs/FG/GCE and selenium concentration was observed between 0.002−5.0 mg/L. The method exhibited a low detection limit of 0.27 μg/L. The proposed method was applied successfully for the determination of selenium in agricultural food (tea, rapeseed sprouts, peanut) and environmental (tap water and lake water) samples. The results showed that the average levels of selenium were 0.04−0.27 mg/kg and not detectable, in agricultural food and water, respectively. Therefore, this method has great potential for the monitor of selenium in food and environmental samples.

Simultaneous and highly sensitive determination of selenium and tellurium species in environmental samples by on-line ionic liquid based in-situ solvent formation microextraction with hydride generation atomic fluorescence spectrometry detection

A novel on-line preconcentration and speciation analysis method for the simultaneous determination of inorganic Se and Te species is presented in this work. The methodology is based on the on-line formation of a hydrophobic ionic liquid (IL) directly in the liquid sample stream of a flow injection system, thus achieving an efficient and rapid extraction of the analytes complexed with ammonium pyrrolidine dithiocarbamate into the finely dispersed extractant droplets, that were then retained in a column filled with cotton. A full study of the chemical and hydrodynamical parameters was developed, including the right selection of the IL used as extractant and its concentration, pH, complexing reagent, sample and ion-exchange reagent volumes and column design. Additionally, a miniaturized external hydride generator was adapted to the spectrometer in order to increase the sensitivity of the atomic fluorescence measurements using only 250 μL of 5 mol L−1 HNO3 in methanol as eluent. The analytical figures of merit obtained for 15 mL of sample included sensitivity enhancement factors of 71, 70, 49 and 40 for Te(IV), Te(VI), Se(IV) and Se(VI), respectively, and limits of detection of 1.8 ng L−1 for both Te species, 2.6 ng L−1 for Se(IV) and 3.2 ng L−1 for Se(VI). After optimization, the method was successfully applied for the analysis of environmental samples: soils and sediments, as well as sea, river, underground and tap water.

Quantitative determination of selenium in the most common food items sold in Egypt

Particular interest in selenium (Se) was generated as a result of clinical studies showing that balanced Se dietary system is very important for many physiological processes. There is no recent information available on the Se content in Egyptian foods. The present study was conducted to measure Se content in different food groups. A cross-sectional study was designed; a total of 87 food items were randomly purchased from the main markets and hypermarkets in Alexandria governorate, then digested by wet ashing procedure and finally analyzed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The highest mean Se value was obtained in protein-rich food followed by nuts and sweetened products (6.8, 6.2, and 5.89 μg/g respectively) shrimps had the highest value among all studied samples (6.8 μg/g), while the lowest one was in soft cheese (0.0036 μg/g). Selenium content in food groups is strongly correlated with food matrix and composition of food items, soil composition, and fortification process.

Fast and simple selenium speciation by solid phase extraction and laser-induced breakdown spectroscopy

The chemical properties including toxicity of selenium depend on the concentration and chemical structure present in the natural environment. Inorganic selenium is more toxic than organic selenium; thus, the accurate determination of inorganic selenium in various sample has been needed. HG-AAS, HPLC-ICP-MS, and GC-MS are the current methods for the determination of inorganic selenium. However, these methods have the disadvantage of expensive equipment, complicated sample preparation, and long analysis time. LIBS coupled with ion exchange membrane was used for the determination of inorganic selenium. The detection limit of inorganic selenium by the analytical method was 11.21 mg/kg, and the recoveries of 50 and 100 mg/kg Se(VI) were 98.5 % and 101.80 %, respectively. The speciation method is cost-effective, simple, and not labor intensive for the quantitation of inorganic selenium.

Zirconium nanoparticles based dispersive solid phase extraction prior to slotted quartz tube-flame atomic absorption spectrophotometry for the determination of selenium in green tea samples

In this study, a novel, easy, rapid and green zirconium nanoparticles (Zr-NPs) based dispersive solid phase extraction (DSPE) method is presented for the precise and sensitive determination of selenium by slotted quartz tube-flame atomic absorption spectrophotometry (SQT-FAAS). Influential parameters of the extraction procedure were optimized by altering one parameter while keeping the other parameters constant. The optimum conditions were selected as 10mg of Zr-NPs, 75s vortex period, and 200µL of concentrated HCl for 30mL of sample/standard solution. The linear range of the developed method was found to be between 25 and 100µg/L, and the respective limits of detection and quantification were 5.3 and 18µg/L. About 415 folds enhancement in detection power was achieved by the optimized method relative to the conventional FAAS. Green tea samples were spiked and used for recovery experiments and the results obtained were between 92 and 102%.

Determination of Selenium in Common and Selenium-Rich Rice from Different Areas in China and Assessment of Their Dietary Intake.

In this study, 41 common rice varieties and 211 selenium-rich rice varieties from ten representative areas in China were collected in 2017–2019. The selenium contents of rice were analyzed with optimized inductively coupled plasma mass spectrometry (ICP-MS). Selenium concentrations of common rice and selenium-rich rice ranges were 0.81–7.26 and 0.76–180.73 µg/100 g, respectively. The selenium contents in selenium-rich rice from different areas were significantly different (p < 0.001) while those in common rice from different areas were not. The selenium-rich rice in Harbin and Keshan showed the lowest selenium level and those from selenium-rich areas (Enshi and Ankang) were highest. Based on the estimation of the risk assessment software @risk7.0 (Palisade Corporation, New York, NY, USA), the consumption of selenium-rich rice can effectively increase dietary selenium intake for the population. However, the risk index of P95 (Percentile 95) selenium exposure at the tolerable upper intake level for children at 2–14 years old exceeded 100%, with potential risk currently. Therefore, the consumption of selenium-rich rice should be properly monitored for young children and adolescents.

Methodological aspects concerning sampling and determination of total selenium and selenium species in geothermal waters

Abstract The work presents the results of geothermal water sample analysis with respect to the determination of total selenium concentration. For this purpose, geothermal water (GT) samples were collected from three different intakes (GT-1, GT-2, GT-3) with similar temperatures of about 85°C. Tests were carried out to see if the methodology of sample preparation influenced total selenium concentration during analysis by inductively coupled plasma mass spectrometry (ICP-MS). Samples (raw and filtered) were preserved with nitric acid (HNO3) and mineralised in the laboratory. From the data obtained it was found that there is no significant difference between total selenium concentration in raw and filtered samples. Following mineralisation, the concentrations in the samples were below the limit of detection or limit of quantification. While different analytical steps or procedures are applied, the results of total selenium concentration can vary. Furthermore, high-performance liquid chromatography coupled with ICP-MS was used for the identification of selenium species. The results revealed that hexavalent selenium – Se(VI) – in the geothermal water was found only in samples collected from the GT-2 and GT-3 intakes.

The challenges of Se quantification in bean samples using line and continuum sources atomic absorption spectrometry

This work demonstrates the challenges for selenium (Se) determination in bean samples using high-resolution continuum source Graphite Furnace Atomic Absorption Spectrometry (HR-CS-GF-AAS) and line source Graphite Furnace Atomic Absorption Spectrometry (LS-GF-AAS). Different chemical modifiers were optimized namely; Ir, Ru, and Pd/Mg nitrates. At selenium contents <5 ng g−1, it cannot be quantified accurately. Spectral interferences of the molecular bands of PO and NO as well as the iron lines with Se line at 196.026 were demonstrated. The noticeable low energy of the continuum source of the HR-CS-GF-AAS at 196.026 nm gives high values of the limits of detection and quantification. The Se limits of detection were found to be 24, 33, and 29 ng g−1 for Ir, Ru, and Pd/Mg modifiers, respectively. In situ trapping hydride generation LS-GF-AAS gives better limits of detection and it reached 30 pg g−1 with Ir modifier.

Trace Elements Content of Some Traditional Plants Used for the Treatment of Diabetes Mellitus

Diabetes is a public health problem that affects life quality. Trace elements have a critical role in the activity and structure of the enzymes involve in carbohydrate metabolism. Many traditional herbs have been used for the treatment and management of Diabetes Mellitus (DM). Anti-diabetic medicinal plants have a significant lowering effect on blood sugar, then assessment of mineral content of these plants has a great value to judge their mechanism of action. Determination of Cobalt (Co), Chromium (Cr), Ferrum (Fe), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Vanadium (V), and Zinc (Zn) values in twenty-eight anti-diabetic plants were conducted and the estimation carried out by atomic absorption spectrophotometry after wet digestion. We found that the levels of Mn, Mo, Co, and Cr were in trace amount, whereas Fe, Se, V and Zn contents were higher. Because of trace elements variations between the studied plants, the hypoglycemic effect of these herbs is not due to a unique element present in the herbs, it rather a synergic effect of several elements might account for the hypoglycemic nature of these plants. Further work is necessary to evaluate this phenomenon.

Towards the abatement of nitrate interference on selenium determination by photochemical vapor generation

A flow injection photochemical vapor generation atomic absorption spectrometry (FI-PVG-AAS) system was developed for selenium determination. The variables of influence of the photochemical generation process were evaluated and optimized. Sample already reduced to the Se(IV) state and mixed with the photochemical reagent (1.5% w/w HCOOH) was irradiated for 3 s. Selenium derivatives were transferred to an externally heated atomization cell by an argon-hydrogen mixture and selenium determined at 196.0 nm. Nitrogen was used as the carrier of the flow injection system. Nitrate is one of the most relevant interferents for the photochemical generation process; it is a very frequent concomitant as nitric acid is added for sample digestion or preservation. Hence, its removal before the vapor generation stage was studied. It was found that up to 3.0% w/w HNO3, it can be eliminated in the reduction stage of Se(VI) to Se(IV) with hydrochloric acid. For higher concentrations (up to 21% w/w HNO3), prior to the reduction step, the addition of 40% w/w H2CO and evaporation almost to dryness was successful for the abatement of the interference. The performance of the method was studied and its applicability evaluated with a Trace Element in Water Certified Reference Material (24.3 μg L−1 – Se, 2.8% w/w HNO3) and a spiked rice-flour microwave-assisted digest (103.1 μg L−1 – Se, 18.5% w/w HNO3).

Determination of Total Selenium and Extractability of Selenium in Commercially-Available Dietary Supplements by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS)

Upper limits for the supplementation of micronutrients are still undecided in many European countries. These limits are of particular interest for selenium because of the narrow range of acceptable intake. Standard analytical protocols to check for compliance must be consistent for a variety of dietary supplements. Emerging products in the evolving market for dietary supplements and over-the-counter (OTC)-medications must be factored in as well. The ICP-MS determination of selenium is well established for scientific research, but a systematic comparison of the operation modes for a realistic set of samples is still missing. In this manuscript, five common cell-techniques for interference removal were approved by a certified reference material (CRM) and applied to a variety of 28 different dietary supplements after microwave digestion. The comparison reveals these operation modes are less consistent for some supplements than for the CRM, whereas 78Se in collision mode was identified as being the most robust. The results for the supplements varied within tolerable limits from the labeled dosage. Extraction with TRIS-buffer was employed as a minimally invasive method to determine the impact in comparison to the total selenium quantification, showing variation among the labeled species (selenomethionine (∼100%), methyl-seleno-cysteine (94%), selenite and selenate (60–100%), selenized yeast (11–28%), spirulina algae (70%)).